Conventionally, a key of a keyboard comprises a keycap, a supporting element, an elastic element, a fixing hook and a key supporting plate. FIG. 1 is a schematic side view illustrating the structure of a key of a conventional keyboard. As shown in FIG. 1, the key comprises a keycap 91, a supporting element 92, an elastic element 93, a fixing hook 94 and a key supporting plate 95. The keycap 91 is disposed over the key supporting plate 95. The elastic element 93 and the supporting element 92 are disposed under the keycap 91. The fixing hook 94 is disposed on the key supporting plate 95. The supporting element 92 is connected with the keycap 91 and the key supporting plate 95. An end of the supporting element 92 is coupled with the fixing hook 94. Consequently, the keycap 91 is supported by the supporting element 92, and the keycap 91 is fixed on the key supporting plate 95 through the supporting element 92. The keycap 91 is pushed upwardly by the elastic element 93. Consequently, a specified height between the keycap 91 and the key supporting plate 95 is maintained.
As mentioned above, the supporting element and the elastic element of the conventional key are fixed on the key supporting plate. In case that the keycap is not depressed, the keycap is continuously supported by the supporting element and the elastic element. Consequently, the height between the keycap and the key supporting plate is fixed. Since the height cannot be changed according to the practical requirements, the thickness of the keyboard is larger. Under this circumstance, it is difficult to store the keyboard and it is not easy to apply the keyboard to the slim-type electronic device. In other words, the conventional keyboard needs to be further improved.